Polyethylene terephthalate (PET) is particularly suitable for the manufacture of fibers, filaments and sheets. PET, however, is not generally suitable for injection molding because of the high molding temperatures (e.g. around 140.degree. C.) and the relatively long molding times required. These severe processing conditions have generally prevented the widespread use of polyethylene terephthalate for injection molding despite the fact that products molded under these severe conditions exhibit high rigidity and high heat distortion temperatures. The high mold temperatures required are beyond the equipment capabilities of many mold shops which have only water heated molds. Such molds are normally capable of temperatures no higher than about 110.degree. C. Thus, wide use of this polymer is restricted not only by the economics of its long processing cycle but also by the inability of many potential molders to process the resin.
In the production of molded polyester resins, it is generally known to add one or more fire retardant additives to enhance the fire resisting properties of the resin. Although it is generally relatively simple to modify a polyester resin to render it substantially nonflammable, one particular problem is the formation of hot drops of resin which form when the product is subjected to a flame source. Obviously, under true fire conditions the formation of such drops could cause further flame spread. (One known method for testing the ability of a material to avoid dripping is UL-94 and UL-94-5V).
One of the objects of the present invention is to provide polyethylene terephthalate compositions which do not readily form drips under UL-94 and UL-94-5V conditions. Another object of the present invention is to provide polyethylene terephthalate compositions which can be molded at lower temperatures and more rapidly than has previously been possible. It is an object of this invention to obtain compositions which additionally have heat distortion temperatures substantially the same as those obtained when molding under the above-noted severe conditions.